echo 0 > /proc/sys/kernel/nmi_watchdogit releases the hardware reservation on the PMUs. This allowsthe oprofile module to grab those PMUs and do its thing.Otherwise oprofile fails to load because the hardware isreserved by the perf_events subsystem.

Tested using:

oprofile --vm-linux --start

and watched it failed when nmi_watchdog is enabled and succeedwhen:

oprofile --deinit && echo 0 > /proc/sys/kernel/nmi_watchdogis run.

Note: this has the side quirk of having the nmi_watchdog latchonto the software events instead of hardware events if oprofilehas already reserved the hardware first. User beware! :-)